This invention relates to heat exchangers and has particular reference to heat-pipe panels for heat exchangers and a method for making them.
A heat-pipe is a totally enclosed, simple, mechanically static device which can transport large quantities of heat over long distances. Basically the heat pipe comprises a pipe-like sealed chamber charged with a vaporizable liquid of four regions: (a) The evaporator in which the working liquid is vaporized by the input heat (b) the vapor transport channel through which vapor flows from the evaporator to the condenser (c) the condenser where the vapor gives up heat and is condensed to liquid, and (d) the liquid transport section in which the liquid condensate flows back to the evaporator.
In some instances circumferential capillary grooves or wicking may be added in the evaporator and/or condenser section to improve liquid wetting or to aid condensate collection. Also, the liquid transport from condenser to evaporator may be aided by wicking which spans the entire length of the pipe from the condensor end to the evaporator end, by capillary grooves or by actually tilting the heat pipe.
Heat pipes are traditionally made as individual tubes and clustered together where additional capacity is required. For better heat transfer to a gaseous medium the tubes are generally provided with closely spaced fins. When a great quantity of heat pipes are required, as in the case of a regenerative heat exchanger between the exhaust flue of a power plant and the air intake to the power plant, the tube-and-fin heat pipe arrangement becomes economically unsuitable.
The present invention is a particularly attractive alternative to the tube-and-fin arrangement from both fabrication and operating viewpoints. In accordance with this invention a heat-pipe panel comprising a plurality of heat-pipes is fabricated by forming parallel furrows in sheet metal plates and then welding or bonding the plates together around each of the furrows to provide the separated chambers which are the individual heat pipes. The heat-pipes may be charged with fluid from a manifold furrow, after which the heat-pipe furrows are sealed by pinching the ends thereof.
If wicking is needed, it is placed in each furrow before assembly of the plates, eliminating the problems associated with drawing a wick into a tubular heat-pipe.
A heat exchanger is constructed by stacking a number of heat-pipe panels of this invention with a separator between the evaporator and condenser end, and the two fluid streams between which heat exchange is to take place being directed over the evaporator and condenser ends. The flat metal between the furrowed heat pipes absorbs or rejects heat and functions similarly to the fins on tubular heat-pipes. The separation of the panels, being significantly greater than the separation of fins on tubes will not become clogged by solid particles in the fluids stream as do the fins. The panels may be easily covered with a protective coating to resist corrosion and/or high temperature if desired. The type and thickness of the protective coating must be carefully selected as to not preclude effective operation of the panels. In conventional tube/fin units the application of a protective coating is not practical due to the close fin spacing. These and other alternative embodiments will be explained in more detail in the descriptive material to follow.